In recent years, high optical performance and also miniaturization and weight reduction of optical systems are demanded also in optical systems such as lenses for digital cameras and optical systems such as projection devices. Thus, lenses with a large aperture and lens balls having a lens surface of a small radius of curvature are increasingly used.
If such a lens ball is used for optical systems, a light beam is incident at a large angle on the periphery of the lens ball. Thus, because the angle of incidence covers a wide range, an antireflection coating in which a dielectric multilayer film is stacked as a single layer or multiple layers cannot sufficiently inhibit reflection, causing harmful light such as ghosts and flares.
To reduce harmful light generated at the periphery of a lens ball, optical systems in which a flare cut is arranged have been known. For example, Example 2 of Patent Literature 1 discloses a flare cut that allows a light flux that forms an image at the image height corresponding to an imaging range to pass through and blocks other light fluxes.